Colorado’s Chromatic Technologies uses fat to create disappearing ink Put your finger on the black spot on the new U.S. postage stamp and the darkness vanishes to reveal an image of the full moon. Magic? No. It’s fat. The nifty thermochromic stamp — created to honor Monday’s total eclipse of the sun and being snapped up by collectors and fun-loving folks everywhere — works like Crisco. At room temperature, the shortening is a gloppy, white paste that liquefies into a clear, shiny soup when warm. The novelty stamp, however, won’t leave fingers oily, black or cold. “They’re esters. But it’s not like the fat right here,” said Lyle Small, pointing to his stomach, which doesn’t jiggle much at all